CHAPTER / CONNECTIONS ACROSS SCALES

Nervous System

Living fibres. Coordinated signals.

A nerve is more than a cable. Explore its bundles and supporting cells, follow roots into regional pathways, and connect anatomical structure with electrical and chemical communication.

Follow tissues, routes and signals →

Chapter overview film planned. No playable video is currently available.

Original opened peripheral nerve exhibit with fascicles, connective support and vessels; illustrative detail, not specimen histology. — Original anatomical exhibit · generated fine detail illustrative

01 / THE TISSUE HIERARCHY

A nerve is organised around bundles.

Epineurium supports the nerve as a whole and between fascicles. Perineurium encloses a fascicle and contributes to a diffusion barrier. Endoneurial tissue supports individual nerve fibres and their local environment. None of these coverings is the axon membrane.

Original opened peripheral nerve trunk with separate fascicles, outer connective support and separate small vessels. — Original source-informed cellular illustration, not microscopy. Visible hierarchy and glial/axon relationships source-verified; fibre counts, lamellar thickness, nuclei, decorative organelles and fine connections illustrative / not independently verified. Human medical review: Not performed.

Between-fascicle tissue: Connective support occupies the spaces between bundles. This connective-tissue region is between bundles, not the pale boundary of one fascicle. No precise point is assigned to an ambiguous generated boundary.

Epineurium

Whole nerve / between bundles

Connective support also accompanies a vascular supply.

Perineurium

Fascicle boundary

A specialised layered boundary, not another myelin sheath.

Endoneurium

Within a fascicle

Local tissue around nerve fibres, not the neuron membrane.

Teaching references: PubMed · Normal peripheral nerve microscopic anatomy · University of Minnesota Histology Guide · peripheral nerve coverings

Follow a source-labelled nerve in three dimensions

Rotate selected native peripheral routes beside their original bone context, choose a source label, hide a layer or isolate a nerve. This separate source reference is not aligned with the adult male or female atlas; its source sex is not established.

Explore the selected peripheral reference →

Root and spinal-ganglion objects can contain multiple levels. A selected trunk is not a complete set of terminal branches. Brain, cranial nerves, a complete spinal cord, fine fascicles and clinical territories are not supplied. Selected skeletal context is incomplete. The chapter explains function; the model supplies broad source shape, not anatomical certification.

02 / CONNECTED TEACHING

A tissue network connects the body.

Distinguish central circuits, peripheral routes and the direction of information.

A network spans organs, tissues and cells.

The brain and spinal cord form the central nervous system. Peripheral nerves connect receptors, muscles, glands and viscera with central circuits. A nerve is a tissue containing many axons and supporting cells; it is not one long neuron.

Central

Brain / spinal cord

Integration occurs through many local and long-distance circuits.

Peripheral

Nerves / ganglia

Axons, glial cells and connective tissues link regional targets.

Functional divisions

Somatic / autonomic / enteric

These describe roles and circuits, not separate isolated bodies.

Teaching references: OpenStax · Nervous organisation · PubMed · Normal peripheral nerve microscopic anatomy

Sensory input and motor output are different directions.

Afferent pathways carry information toward central circuits. Efferent pathways carry commands toward effectors. A mixed peripheral nerve contains different axons serving these roles; one axon does not routinely alternate between being sensory and motor.

Input, integration and output

Start in a tissue, follow an incoming axon, then ask where a response is assembled. Sensory input and motor output travel in different axons.

Original realistic skin cutaway: fine gold sensory branches rise from a dermal nerve toward free terminal endings in superficial skin; red capillary loops are distinct. No sensory soma is in the skin. — Original generated anatomical teaching illustration, not microscopy. Representative free endings; colour distinguishes nerve from vessel, not a molecular receptor subtype. Cell counts, layer thickness and terminal density are not measurements.

Cyan: a representative sensory direction away from the skin endings. Not every skin ending detects the same stimulus.

Stimulus → electrical changeMechanical, thermal or chemical conditions can change a sensory ending’s membrane current. A graded receptor potential can bring a spike-generating region to threshold; stimulus information is carried by patterns of action potentials, not by a piece of the stimulus travelling inside the nerve.

One route, a soma beside itThe peripheral and central processes of a typical primary somatic sensory neuron meet at a T junction. Its soma lies in a sensory ganglion. The dorsal-root ganglion is not the central synaptic integration station.

Into the cord. Out toward a target.

Original oblique spinal preparation: posterior rootlets enter a ganglion above separate anterior rootlets; the roots join a short mixed nerve before branching into posterior and anterior rami. — Original AI-assisted anatomical illustration, not a specimen or clinical scan. Posterior is above; anterior below. One representative level, not an exact vertebral-level or surgical map. Fine rootlets, horn nuclei, meningeal boundaries and communicating branches are not certified or completely shown.

Cyan: toward the cord through the posterior root. Gold: outward through the anterior root. Arrows follow broad root corridors, not a verified individual fascicle or intramedullary synapse. Both rami remain mixed.

Integration changes the responseA cutaneous withdrawal response recruits spinal interneurons and motor neurons; it is not a one-synapse skin-to-muscle shortcut. Excitation of selected muscles, inhibition of antagonists and signals to higher centres involve related but distinct circuits. The generated cord section does not locate those individual synapses.

Output meets a different tissueA lower motor neuron’s axon leaves toward skeletal muscle, where a specialised neuromuscular junction uses acetylcholine to initiate endplate depolarisation. This is a different cellular interface from a skin receptor. Reflex action can occur without a conscious decision, while descending circuits can modify the response.

Inspect root and ramus structure →Reflex circuits and their variations →See the retained detailed motor endplate →Compare the sensory T junction →

Teaching focus: Sensory input — Receptor-related axons carry information toward central circuits.

Sensory input

Receptor-related axons carry information toward central circuits.

Integration

Local and long-distance circuits combine inputs and internal state.

Output

Somatic or autonomic efferent routes influence their targets.

Source relationships checked 16 October 2026: sensory endings · motor responses and reflexes · peripheral routes · autonomic ganglia and varicosities. AI-assisted source and structure checks, not physician review.

Teaching references: OpenStax · Nervous organisation · OpenStax · Peripheral nerve organisation

Follow selected routes in body context.

Locate central tissue within its bony protection, then follow selected peripheral routes in real body context. A larger-scale window distinguishes the cord ending from the roots below.

One body. Different neural compartments.

Start with the brain and cord, then find routes travelling into the limbs. The regional nerves lie among real muscles and bones; they are not single neurons drawn across an empty silhouette.

Original posterior anatomical illustration with an opened skull and vertebral canal, brain and spinal cord, separate descending lower roots and selected nerve routes in the limbs. — Posterior view. Bone and muscle are selectively opened to show different depths together. This original generated preparation is not a specimen, clinical scan, complete nerve inventory or exact vertebral-level map. Selected gold routes do not resolve every named branch, plexus contribution or skin territory.

Locate central tissueCompare the brain with the cord in the opened vertebral canal. The cord is neural tissue; the surrounding vertebral column is bone. Connections within both central structures are more complex than the selected surface view can show.

Look closer · a cord is not the roots below it.

Locate the smooth taper, then the separate fibres within the lower canal. This small window is limited to its original pixel detail; the inspection view retains that limit instead of stretching the anatomy. A genuinely higher-detail local preparation remains to be supplied.

Original-resolution window of the same anatomical master at the upper lumbar taper and separate descending cauda-equina roots within an opened canal. — 130 × 205 source-pixel window from the same posterior preparation; display size is capped to avoid invented or blurred detail. The smooth cord tapers above separate descending roots. The root bundle is not another solid spinal cord. Exact segment counts, tiny root attachments, meninges and individual exit levels are not resolved by this view.

Central tissue is surrounded by a different supporting skeleton.

The brain and spinal cord form the central nervous system. The skull and vertebral column protect that tissue; they are not themselves nervous structures. The opened posterior view lets you compare the brain, the cord within the canal and nerves travelling outward into the body. Local spinal circuits can organise responses as well as passing information along longer pathways.

Evidence: OpenStax · central and peripheral organisation · UTHealth Neuroscience Online · spinal cord anatomy, sections 3.1–3.4

A longer vertebral column does not mean a longer spinal cord.

In an adult, the cord usually ends around the first or second lumbar vertebra. Lower nerve roots continue down within the canal before reaching their exits. Those separate roots form the cauda equina: they are peripheral nerve roots, not a solid continuation of the cord. Spinal cord segments and the bones beside them therefore do not keep a one-to-one alignment down the whole back.

Evidence: UTHealth Neuroscience Online · spinal cord anatomy, sections 3.1–3.4

One visible nerve contains many different fibres.

The large peripheral trunks are tissue bundles, not single neurons. Supporting cells, connective coverings and blood vessels accompany their axons. Sensory and motor axons can share a mixed nerve while serving different directions. Regional plexuses redistribute axons into routes to a limb; an intersecting line alone does not identify a synapse or a neuronal cell body.

Evidence: OpenStax · nerve tissue and peripheral connections

Deeper learning · route, function and scale are different questions

Central versus peripheral describes anatomical organisation. Sensory versus motor describes the direction and role of particular axons. Somatic, autonomic and enteric learning adds further circuit distinctions; the posterior limb view is not a complete map of visceral or cranial pathways.

A lower root can descend inside the vertebral canal before leaving it. A named peripheral nerve can then contain fibres redistributed from several spinal levels. Neither a nerve’s position beside a bone nor the colour used in a teaching illustration establishes its complete root supply.

Compare roots, sensory ganglion and mixed nerve → · Trace the brachial network at a larger scale → · Inspect the posterior lower-limb preparations → · Change to autonomic cellular relays →

Explore the connected central anatomy →

Directed source and gross-structure checks: 16 October 2026. Original generated illustration, with separate editable names, anchors and interaction. Retained native-source references below preserve their own licensed geometry. Fine anatomy, complete cranial and visceral routes, physical-phone and physician review are not certified.

Retained native regional reference · selected peripheral routes

This source-native overview locates limb routes and spinal sensory ganglia. It deliberately omits brain, cranial nerves and many smaller branches: a selected peripheral reference is not a complete nervous-system atlas.

Peripheral routes in skeletal context; selected cream-coloured nerve routes in translucent native skeletal context. — Retained source-native supporting reference; native topology unchanged. Selected native peripheral routes; pale bones are ghosted for orientation. No independent deformation; incomplete branch coverage and fine source tube/surface detail remains illustrative / not independently verified. BodyParts3D — DBCLS (CC BY-SA 2.1 Japan); Z-Anatomy (CC BY-SA 4.0); FBX: Lluís Vinent Juanico. AllHumanBody render and changes: CC BY-SA 4.0. Full provenance in Sources below.

Brain: central anatomy →

Teaching references: NCBI · Brachial plexus · NCBI · Thigh nerves · Z-Anatomy · Source licence and third-party exclusions

03 / CONNECTED TEACHING

Several boundaries serve different jobs.

Move from the whole nerve to one fascicle, then distinguish axons from their supporting cells.

One bundle can contain different fibres.

A fascicle contains axons with their Schwann-cell context; a nerve can contain myelinated and unmyelinated fibres. Fascicle number and packing vary by nerve and along its course. The supporting illustration expands spaces to explain organisation.

Original closer single fascicle: boundary, endoneurial connective tissue and central axons within pale myelin profiles. — Original source-informed cellular illustration, not microscopy. Visible hierarchy and glial/axon relationships source-verified; fibre counts, lamellar thickness, nuclei, decorative organelles and fine connections illustrative / not independently verified. Human medical review: Not performed.

Source-informed educational illustration, not histology. Invented packing, repeated profiles and diameters are not measured anatomy or a universal fascicle count.

Teaching references: PubMed · Normal peripheral nerve microscopic anatomy · NLM · Myelin formation and structure · University of Minnesota Histology Guide · peripheral nerve coverings

Shape is related to the path a cell serves.

Motor neurons and many central neurons are multipolar. Many primary sensory neurons are pseudounipolar, with a peripheral and central process linked to their cell body. Bipolar cells occur in specialised sensory systems. These are examples, not a complete taxonomy.

Different cell shapes serve different routes

Three separate anatomical examples. Trace a process before naming its direction.

Three independent detailed neuronal examples on one original plate: multipolar above, pseudounipolar with soma off the continuous T route in the middle, and bipolar below. No inter-row connections. — Original generated medical teaching illustration, not microscopy. Broad relationships source-checked; organelle counts, protein shapes and dimensions are not measurements. Labels and mechanism arrows are independently editable. Human medical review not performed.

Multipolar · many inputs, one axonal route

Many central and motor neurons have this arrangement. Inputs combine across dendrites and soma; action potentials commonly begin near the axon initial segment. This is one example, not a universal cell silhouette.

Pseudounipolar · soma beside the route

In a typical primary sensory ganglion neuron, one process leaves the soma and divides. The peripheral and central branches form a continuous route; the soma is not a synaptic relay. Left is peripheral context; right is central context in this example.

Bipolar · processes at opposite poles

Bipolar neurons occur in specialised sensory pathways, including retinal circuits. This shape is not a specific retinal layer map.

Teaching focus: Multipolar example — Dendritic inputs and a separate axonal route; not every cell has the same branching.

Multipolar example

Dendritic inputs and a separate axonal route; not every cell has the same branching.

Pseudounipolar example

Primary sensory soma branches off the continuous peripheral-to-central route; no relay synapse is shown at the soma.

Bipolar example

Distinct processes occur in specialised sensory contexts such as the retina.

Mechanism checked 16 October 2026: cell shapes and myelin · channels and propagation · chemical transmission. Source-based AI-assisted checks are not physician review.

Teaching references: OpenStax · Neurons and supporting cells

Supporting cells actively maintain neural tissue.

Schwann cells support peripheral axons. Oligodendrocytes myelinate central axons. Astrocytes help regulate local tissue conditions; microglia participate in immune surveillance. Ependymal cells line ventricular surfaces. These roles are not interchangeable.

Schwann cells

Peripheral nerve

Myelinating and nonmyelinating relationships differ.

Oligodendrocytes

Central nervous system

One cell can supply internodes on multiple axons.

Other central glia

Astrocytes / microglia / ependyma

Different support, immune and lining roles; no fixed neuron-to-glia ratio.

Teaching references: NLM · Neuroglia terminology and roles · NLM · Myelin formation and structure

04 / CONNECTED TEACHING

Similar insulation. Different cellular arrangements.

Compare successive peripheral internodes with the branching support of a central glial cell.

One Schwann cell makes one myelinated internode.

For a myelinated peripheral fibre, an individual Schwann cell wraps one axon segment. Successive cells form successive internodes. Gaps between internodes expose nodal membrane; the axon itself remains continuous.

Continuous golden axon passes through two separately wrapped Schwann-cell myelin internodes with an enlarged nodal region between them. — Original source-informed cellular illustration, not microscopy. Visible hierarchy and glial/axon relationships source-verified; fibre counts, lamellar thickness, nuclei, decorative organelles and fine connections illustrative / not independently verified. Human medical review: Not performed.

The gap is enlarged for teaching. This is not an exposed cable break, measured nodal length or literal electron micrograph.

Teaching references: NLM · Myelin formation and structure · Southern Illinois University · neurons and supporting cells

Central myelin uses a different cellular arrangement.

An oligodendrocyte can extend processes to internodes on different axons. The relationship differs from a myelinating Schwann cell. Exact numbers vary; the illustration does not establish a universal number of axons per cell.

An oligodendrocyte extends separate processes to myelin internodes on multiple continuous axons, distinct from the axons themselves. — Original source-informed cellular illustration, not microscopy. Visible hierarchy and glial/axon relationships source-verified; fibre counts, lamellar thickness, nuclei, decorative organelles and fine connections illustrative / not independently verified. Human medical review: Not performed.

Brain: white matter and glial context →

Teaching references: NLM · Myelin formation and structure · NLM · Neuroglia terminology and roles · Southern Illinois University · neurons and supporting cells

05 / CONNECTED TEACHING

Gradients, channels and junctions carry information.

The fibre remains continuous. Supporting mechanism views explain voltage and transmission in the living tissue.

Voltage comes from gradients and selective permeability.

A resting membrane potential reflects ion gradients and membrane permeability. Ion pumps maintain gradients over time. Channels change permeability rapidly during signalling; the sodium–potassium pump does not directly generate each upstroke of an action potential.

Selective permeability changes voltage

Read across a real membrane boundary: a lipid barrier, selective channels and a separate energy-driven pump.

Realistic exposed axolemma: phospholipid head layers and tail core, open pore, closed channel and separate pump protein, extracellular fluid above and axoplasm below. — Original generated medical teaching illustration, not microscopy. Broad relationships source-checked; organelle counts, protein shapes and dimensions are not measurements. Labels and mechanism arrows are independently editable. Human medical review not performed.

Gold arrow illustrates inward current through the open channel during a typical sodium-driven depolarising phase. It is not an arrow through the lipid core or a universal direction for every ion.

A selective barrier: lipid tails face inward; heads face the aqueous compartments. Ion distributions and relative permeability, especially resting potassium permeability in many neurons, contribute to membrane voltage.

A rapid change: gates alter permeability. In a typical spike, sodium entry drives the upstroke; sodium-channel inactivation and potassium conductance contribute to recovery. The qualitative waveform remains in the next lesson.

Maintaining the conditions: ATP-dependent pumps sustain gradients over time. They do not directly create each millisecond upstroke. Shown proteins are illustrative classes, not verified molecular structures; ion counts and colours are not measured concentrations.

Teaching focus: Gradients — Different ion distributions are maintained over time; symbols are not measured counts.

Gradients

Different ion distributions are maintained over time; symbols are not measured counts.

Channels

Selective leak and gated channels permit current according to electrochemical conditions.

Maintenance

Pumps sustain gradients; this is not the millisecond mechanism generating every spike upstroke.

Mechanism checked 16 October 2026: cell shapes and myelin · channels and propagation · chemical transmission. Source-based AI-assisted checks are not physician review.

Teaching references: NLM · Action potentials

A local response can vary in size.

Receptor and synaptic potentials can vary with input. Excitatory and inhibitory effects combine across space and time. Whether a cell reaches firing threshold depends on its state and inputs; a stronger stimulus is not simply a taller action potential.

Graded response

Receptor / synaptic regions

Amplitude varies; local changes can weaken with distance.

Summation

Inputs in space and time

Timing and location affect how signals combine.

Spike output

Excitable membrane

Frequency and timing can convey information; all-or-none is a scoped teaching model.

Teaching references: NLM · Action potentials · NLM · Chemical synaptic transmission

Channels change state through a repeating cycle.

In a typical neuronal action potential, voltage-gated sodium-channel activation drives rapid depolarisation. Sodium-channel inactivation and potassium conductance contribute to repolarisation. Recovery creates refractory behaviour. Channel details vary by cell type.

A qualitative action-potential sequence

Supporting educational diagram; not literal regional anatomy, microscopy or a measured recording. Essential explanations remain visible. Select only to highlight a step.

At narrow widths, scroll the supporting diagram sideways for full-size labels.

Depolarisation

Typical neuronal sodium-channel activation drives a rapid upstroke.

Repolarisation

Sodium inactivation and potassium conductance contribute to voltage recovery.

Recovery

Refractory behaviour changes immediate re-excitability. No universal times or voltages are plotted.

Teaching references: NLM · Action potentials

Myelin changes where the signal is regenerated.

Local current spreads between nodes in a myelinated axon; action potentials are regenerated at nodes. Unmyelinated axons regenerate along their excitable membrane. Saltatory conduction does not mean particles or whole spikes leap across empty axon gaps.

The axon remains continuous

Follow the continuous gold axon. Wrapping stops at nodes; the axon does not.

Three peripheral Schwann-cell internodes on one intact axon; central opened wrap reveals compact membrane layers. — Original generated medical teaching illustration, not microscopy. Broad relationships source-checked; organelle counts, protein shapes and dimensions are not measurements. Labels and mechanism arrows are independently editable. Human medical review not performed.

Gold arrows: local current along the axon, and Na⁺ entry at an exposed node. No particle leaps across a broken fibre.

Closer: where wrapping ends

Enlarged node of Ranvier between opened myelin sheath ends, with axon continuous beneath. — Same original master, enlarged at a different scale. Myelin ends, axon membrane continues. Fine paranodal folds are illustrative, not a molecular junction model.

Compare: without compact myelin

Supported unmyelinated axon, shown without compact wrapping. — Same original master, distinct comparison. Unmyelinated peripheral axons can still have nonmyelinating Schwann support; this is not every Remak-bundle arrangement.

Under myelin: insulation reduces current loss and effective membrane capacitance. Local current in the continuous axon helps bring the next node toward threshold.

At nodes: concentrated voltage-gated sodium channels support regeneration of the action potential. Internodes are shortened and nodes enlarged here; no speed or dimension is measured.

Different glia: each myelinating Schwann cell serves one peripheral internode. A CNS oligodendrocyte can myelinate several internodes; existing cell-comparison plates above retain that distinction.

Teaching focus: Internode — Local current spreads under myelin; the axon is not interrupted.

Internode

Local current spreads under myelin; the axon is not interrupted.

Node

Excitable nodal membrane regenerates the action potential.

Sequence

Successive regeneration supports propagation; this is not a particle jumping a gap.

Mechanism checked 16 October 2026: cell shapes and myelin · channels and propagation · chemical transmission. Source-based AI-assisted checks are not physician review.

Teaching references: NLM · Myelin formation and structure · NLM · Action potentials

A junction can translate electrical activity into chemistry.

At a chemical synapse, calcium entry into a presynaptic ending supports transmitter release. Receptors change the postsynaptic response. Transmitter is cleared through several mechanisms. Electrical synapses use gap junctions and are a different arrangement.

Electrical arrival, chemical release, receptor response

Read from the upper terminal, across the cleft, to the lower receiving membrane.

Realistic cutaway of terminal above and separate dendritic spine below: vesicles, one membrane-connected fusion pore, extracellular cleft and postsynaptic receptors. — Original generated medical teaching illustration, not microscopy. Broad relationships source-checked; organelle counts, protein shapes and dimensions are not measurements. Labels and mechanism arrows are independently editable. Human medical review not performed.

Upward gold arrow: Ca²⁺ entry through presynaptic channel context. Downward arrow: released transmitter into the cleft. Vesicles do not cross the gap.

Arrival → release: terminal depolarisation opens voltage-gated calcium channels. Incoming calcium supports vesicle fusion with the presynaptic membrane and release of its contents.

Release → response: transmitter binds receptors. This illustration scopes an ionotropic receiving junction; other receptors work through intracellular signalling. The postsynaptic effect depends on the receptor and ion gradients, and need not trigger a new spike.

Ending the signal: diffusion, transporter uptake and/or enzyme action clear transmitter according to the synapse. Electrical synapses instead pass current through gap junctions; they are not pictured here.

Teaching focus: Presynaptic ending — Depolarisation opens voltage-gated calcium channels and calcium supports vesicle release.

Presynaptic ending

Depolarisation opens voltage-gated calcium channels and calcium supports vesicle release.

Cleft

Released transmitter crosses a small extracellular space.

Postsynaptic membrane

Receptor activation changes the response; it does not guarantee the next cell fires.

Mechanism checked 16 October 2026: cell shapes and myelin · channels and propagation · chemical transmission. Source-based AI-assisted checks are not physician review.

Muscles: neuromuscular junction →

Teaching references: NLM · Chemical synaptic transmission

06 / CONNECTED TEACHING

Roots join before mixed branches separate.

Locate the sensory ganglion, efferent root and short common nerve. A posterior ramus is not a posterior root.

Roots separate direction before a nerve becomes mixed.

Dorsal roots carry sensory axons into cord context; dorsal-root ganglia hold primary sensory cell bodies. Ventral roots carry efferent axons outward. After roots join, a short spinal nerve is mixed. The rendered source aggregates are regional, not a labelled single spinal level.

Inspect the retained root preparation with sensory and motor directions →

The posterior root carries incoming sensory fibres and has a ganglion containing their cell bodies. The separate anterior root carries efferent fibres outward; at applicable levels these include visceral as well as skeletal motor output.

After the roots unite, sensory and motor fibres share a short spinal nerve. Its posterior and anterior rami are both mixed. Their names describe where they go, not a split into purely sensory and purely motor nerves.

The preparation explains joining and branching. It does not establish a surgical exit point, vertebral level, complete meningeal envelope or every communicating branch. The native regional reference below shows a different scale.

Teaching references: UTHealth Neuroscience · spinal cord and nerve relationships · UAMS · nerves of the back

Roots and sensory ganglia in a regional window; selected cream-coloured nerve routes in translucent native skeletal context. — Retained source-native supporting reference; native topology unchanged. Selected native peripheral routes; pale bones are ghosted for orientation. No independent deformation; incomplete branch coverage and fine source tube/surface detail remains illustrative / not independently verified. BodyParts3D — DBCLS (CC BY-SA 2.1 Japan); Z-Anatomy (CC BY-SA 4.0); FBX: Lluís Vinent Juanico. AllHumanBody render and changes: CC BY-SA 4.0. Full provenance in Sources below.

Brain: spinal cord section and reflex circuit →

Teaching references: OpenStax · Peripheral nerve organisation · NCBI · Dorsal root ganglion

A ramus is not a dorsal or ventral root.

After a spinal nerve forms, its dorsal and ventral rami both contain mixed fibres. Dorsal rami supply deep back and associated skin; ventral rami supply anterolateral trunk and limbs. Do not label a dorsal ramus as purely sensory or a ventral ramus as purely motor.

Root direction differs from ramus composition

Supporting educational diagram; not literal regional anatomy, microscopy or a measured recording. Essential explanations remain visible. Select only to highlight a step.

At narrow widths, scroll the supporting diagram sideways for full-size labels.

Dorsal root

Sensory axons enter; primary sensory somata lie in dorsal-root ganglia.

Ventral root

Efferent axons exit toward skeletal or autonomic pathways.

Mixed nerve and rami

After roots join, both dorsal and ventral rami carry mixed fibres. Ganglion is not drawn as a synaptic relay.

Teaching references: OpenStax · Peripheral nerve organisation

Thirty-one pairs connect with the spinal cord.

The usual arrangement comprises eight cervical, twelve thoracic, five lumbar, five sacral and one coccygeal pair. Cord segments, exiting nerves and vertebrae do not stay at matching heights through the adult column. Descending lower roots form cauda-equina context.

Cervical

8 pairs

C8 exits between C7 and T1 vertebrae.

Thoracic

12 pairs

Many ventral rami follow segmental thoracic routes.

Lower regions

5 lumbar / 5 sacral / 1 coccygeal

Lower roots descend before leaving the vertebral canal.

Teaching references: NCBI · Spinal cord anatomy

07 / CONNECTED TEACHING

Plexuses redistribute fibres to regional targets.

Licensed native-source references locate selected routes. They omit many surrounding tissues and do not replace a complete anatomical atlas.

A plexus redistributes axons; it is not a new relay.

Anterior rami contribute fibres to limb plexuses. Bundles regroup into trunks, divisions, cords and branches in the brachial plexus. These junctions reorganise axons; they are not ganglia where every fibre synapses.

Trace a contribution into a named nerve.

Original expanded tissue preparation of a typical brachial plexus. Five anterior-ramus inputs become three trunks, six divisions and three cords; median roots unite, while axillary and radial arise independently from the posterior cord. — Original generated expanded nerve preparation, not in-situ anatomy, microscopy or a surgical map. Main connections independently traced against sources; smaller collateral branches are omitted. Spacing and generic muscle/bone context are not measured. Warm/cool nerve colours distinguish routes, not myelin, sensory or motor classes.

Musculocutaneous · Lateral cordThe lateral cord supplies a separate musculocutaneous route. It serves major anterior-arm muscles and continues into lateral-forearm sensory context; it is not a branch of the median nerve.

5 anterior ramiC5–T1 contributions
3 trunksUpper, middle and lower unions
6 divisionsEach trunk divides in two
3 cordsDivisions regroup
5 main terminal nervesDifferent routes to targets

A plexus reorganises axons. It does not turn each meeting point into a synapse. Follow the five named branches above, then inspect the two places where fibres regroup.

Closer · the three trunks

Enlarged proximal region of the same text-free master: C5 and C6 unite, C7 continues alone, C8 and T1 unite. — Same master, enlarged proximal preparation. These plexus “roots” are anterior rami. No dorsal-root ganglia or relay synapses are being identified.

Closer · divisions into cords

Enlarged middle of the same preparation, showing anterior and posterior division routes and three cord recombinations. — Same master, expanded central connections. Crossings in separate planes are not junctions. Posterior routes are cool-tinted only to aid tracing. The artery-relative cord names require the separate spatial view below.

A root here is an anterior ramus. The separate sensory posterior root and efferent anterior root have already united into a spinal nerve before that nerve branches into rami. Plexus roots should not be confused with the cord’s motor rootlets.

The middle contribution stays distinct. In the typical pattern, C5 and C6 form the superior trunk, C7 continues into the middle trunk, and C8 with T1 form the inferior trunk. Each trunk supplies anterior and posterior divisions.

Recombination is selective. The upper two anterior divisions form the lateral cord; the lower anterior division continues as the medial cord. All three posterior divisions contribute to the posterior cord. The median roots subsequently unite, while axillary and radial branch separately from the posterior cord.

Regional position is a different question. Trunks are generally above the clavicle, divisions pass behind it, and cords occupy the axillary region. The network above is spread out to expose connections; use the retained regional reference and the separate artery view for spatial context.

Why “lateral”, “medial” and “posterior”?

Cord names refer to their typical relationship to the second part of the axillary artery, rather than to the reader’s screen. This separate, expanded tissue window establishes directions; it is not the same magnification or a registered slice of the network above.

Anterior ↑← Lateral · Medial →Posterior ↓

Original expanded transverse tissue window: one central red artery with a lateral cord at image left, medial cord at image right and posterior cord below in the declared anatomical orientation. — Original generated representative transverse organisation, not CT, MRI, a specimen or a certified exact slice through the artery’s second part. Selected structures only: the axillary vein and other regional structures are not fully shown. Spacing, fascicle counts and fine surrounding tissue are illustrative, not measurements.

Deeper learning · a named nerve is not one spinal segment

A terminal nerve can contain axons from several spinal levels. A sensory dermatome describes a spinal-root relationship, whereas a named peripheral nerve’s skin territory combines its own branches and root contributions. Neither map is a perfectly sharp boundary in every person. Anatomical variations also change branching and contributions; this typical preparation is not a diagnostic map.

Compare dermatome, peripheral territory and myotome →Continue into arm, forearm and hand routes →

Directed source checks · 16 October 2026: UCSF · brachial plexus organisation · Texas Tech · axillary cords and branches · UAMS · upper-limb nerve origins and targets. Original generated teaching art; source and image checks are AI-assisted, not physician review.

Retained native regional reference · locate the plexus

Right brachial plexus; selected cream-coloured nerve routes in translucent native skeletal context. — Retained source-native supporting reference; native topology unchanged. Selected native peripheral routes; pale bones are ghosted for orientation. No independent deformation; incomplete branch coverage and fine source tube/surface detail remains illustrative / not independently verified. BodyParts3D — DBCLS (CC BY-SA 2.1 Japan); Z-Anatomy (CC BY-SA 4.0); FBX: Lluís Vinent Juanico. AllHumanBody render and changes: CC BY-SA 4.0. Full provenance in Sources below.

Typical major contributions are C5–T1. Source anatomy and individual branching vary; the view does not establish a universal surgical pattern.

Teaching references: NCBI · Brachial plexus

The named stages explain where fibres regroup.

C5–C6 contributions usually form the superior trunk, C7 the middle trunk and C8–T1 the inferior trunk. Trunks divide; divisions combine into cords. Cords are named relative to axillary-artery context. Axillary and radial nerves arise from the posterior cord, not one from the other.

Roots

Anterior rami

These plexus roots are not the cord’s separate dorsal/ventral roots.

Trunks → divisions

Trunks above · divisions behind the clavicle

Three trunks each divide into anterior and posterior divisions.

Cords → branches

Axillary regional context

Lateral, medial and posterior cords contribute to terminal branches.

Teaching references: NCBI · Brachial plexus

Named limb nerves connect many targets.

Median, ulnar and radial nerves take different courses and carry different branch combinations. Regional anatomy is more useful than treating the hand as three perfectly separate coloured zones. Sensory territories overlap and vary.

One elbow. Different nerve routes.

Use the bone and muscle context to distinguish a nerve passing behind a prominence from a nerve dividing into superficial and deep branches. These are separate selected views, not two sides of one registered scan.

Medial side · a route behind bone

Original posteromedial elbow preparation showing the ulnar nerve passing between the humeral medial epicondyle and olecranon before continuing toward proximal forearm tissue. — Original generated selected preparation, not clinical imaging or a surgical map. The opened tissue exposes the posterior groove. Distal muscle heads and the complete cubital-tunnel roof are not individually certified or exhaustively shown.

Locate the posterior grooveThe nerve passes behind the medial epicondyle, between that prominence and the olecranon. This bony relationship is different from the radial nerve’s lateral-elbow branching.

Lateral side · one parent, different branches

Original detailed lateral-elbow tissue window. A yellow radial nerve divides near the elbow; its superficial branch continues distally while the deep branch enters an opened proximal muscle region around the radius. — Original generated teaching anatomy, not a specimen or surgical map. A selected lateral-elbow preparation exposes major branch relationships. Exact muscle attachments, the complete passage through supinator, the arcade of Frohse and a precise posterior-interosseous naming boundary are not identified. The posterior humeral course is outside this view.

Find the splitThe radial nerve has already travelled through the arm. Near the lateral elbow it divides: a common origin does not mean the two branches have the same targets.

Origin is not the same as destination. The ulnar nerve arises from the medial cord; the radial nerve from the posterior cord. Each carries many axons, with branches to different targets. A change in bundle direction does not create a relay synapse. Return to the plexus connections →

Move distally without inventing one common tunnel. At the wrist the median nerve travels beneath the flexor retinaculum in the carpal tunnel. The ulnar nerve uses a separate, more superficial ulnar-side route. A high-detail new wrist window is still in preparation; the elbow views above do not demonstrate those wrist relationships. Continue with existing flexor and pulley anatomy →

Position explains vulnerability, not a diagnosis. A superficial nerve beside a bony prominence and a branch travelling through muscle meet different mechanical surroundings. Symptoms depend on the level, fibres and severity involved; these illustrations cannot locate a lesion in an individual person. Distinguish nerve territory and spinal dermatome →

Deeper learning · what this pair of views cannot show

The radial nerve’s posterior humeral route lies outside the selected elbow view. The complete deep-branch passage through supinator, precise collateral branches, muscle-attachment details and cubital-tunnel roof are not mapped exhaustively. Natural variation also changes branching and territories. The retained licensed native regional reference below gives broader context at a different scale.

Names, short explanations, semantic anchor IDs and focus geometry are independent of the text-free medical images. The same figure data feed body, enlargement and accessible descriptions. English remains the public language.

Directed checks · 16 October 2026: Texas Tech · forearm and radial branches · Texas Tech · regional relationships · UAMS · upper-limb nerve origins and roles. Original generated teaching art; source checks and image review are AI-assisted, not physician approval.

Retained native regional reference · arm and hand routes

Right arm, forearm and hand nerves; selected cream-coloured nerve routes in translucent native skeletal context. — Retained source-native supporting reference; native topology unchanged. Selected native peripheral routes; pale bones are ghosted for orientation. No independent deformation; incomplete branch coverage and fine source tube/surface detail remains illustrative / not independently verified. BodyParts3D — DBCLS (CC BY-SA 2.1 Japan); Z-Anatomy (CC BY-SA 4.0); FBX: Lluís Vinent Juanico. AllHumanBody render and changes: CC BY-SA 4.0. Full provenance in Sources below.

Hand, Foot & Arches →Muscles & Movement →

Teaching references: NCBI · Upper-limb nerves · NCBI · Brachial plexus

A dermatome differs from a named-nerve territory.

A dermatome is skin associated with a spinal sensory root. A peripheral cutaneous nerve can contain fibres from several roots. A myotome concerns segmental muscle supply. Maps are useful approximations with overlap, not exact boundaries on every person.

Dermatome

Spinal root relationship

Overlapping segmental sensory context.

Peripheral territory

Named nerve relationship

Fibres may derive from multiple root levels.

Myotome

Segmental motor contribution

Muscles commonly receive more than one segmental contribution.

Teaching references: NCBI · Dermatomes · OpenStax · Peripheral nerve organisation

Anterior and medial thigh routes have different roles.

Femoral branches supply major anterior-thigh muscles and sensory routes. Obturator branches contribute to medial-thigh adductors. Their native paths through pelvic and femoral context are retained; surrounding muscles are omitted rather than invented.

Right anterior thigh routes; selected cream-coloured nerve routes in translucent native skeletal context. — Retained source-native supporting reference; native topology unchanged. Selected native peripheral routes; pale bones are ghosted for orientation. No independent deformation; incomplete branch coverage and fine source tube/surface detail remains illustrative / not independently verified. BodyParts3D — DBCLS (CC BY-SA 2.1 Japan); Z-Anatomy (CC BY-SA 4.0); FBX: Lluís Vinent Juanico. AllHumanBody render and changes: CC BY-SA 4.0. Full provenance in Sources below.

Teaching references: NCBI · Thigh nerves

Sciatic components continue toward leg and foot.

The sciatic route contains tibial and common fibular components. Their separation level varies. Tibial branches serve posterior-leg and plantar-foot context; fibular branches serve anterior/lateral-leg and dorsal-foot context. Sensory branches are not synonymous with motor compartments.

Place the route. Then follow its two components.

These posterior right-sided views use different scales. The first locates a proximal route beneath reflected gluteal tissue; the second reveals how two major components continue beyond the thigh.

Hip to thigh · a deep, continuous route

Original posterior right gluteal teaching preparation with gluteus maximus reflected. The sciatic nerve emerges below piriformis and descends between the ischial tuberosity and greater trochanter toward posterior thigh tissue. — Original generated selected preparation, not a specimen or surgical map. One common pattern is illustrated. The visible sacral side has four posterior openings; the opposite side and exact root-to-foramen mapping are not shown. Fine muscle attachments and every small nerve branch are not certified.

Locate the proximal routeIn the illustrated common arrangement, the sciatic nerve leaves the pelvis below piriformis. Some people have a higher separation or a different muscle relationship; the picture is not an invariant pattern.

Knee to leg · central and lateral continuations

Original posterior right knee and proximal calf preparation. A representative sciatic separation gives a central tibial nerve and a lateral common fibular nerve, which curves around the fibular neck. — Original generated selected neuro-musculoskeletal view, not clinical imaging or a fixed branching-level standard. Medial is left; lateral is right. Smaller collateral nerves and popliteal artery/vein are omitted. Distal fibular branches and exact muscle attachments are not completely shown.

Distinguish the componentsA visible separation reorganises the outer bundles; it is not a synaptic relay. Its height varies from the pelvis or thigh to the region above the knee. This image chooses one representative level.

A shared route carries several spinal contributions. The usual sciatic contribution spans L4–S3 through the sacral plexus. Axons travel together without becoming one neuron. A named peripheral nerve and a spinal-root territory therefore answer different questions. Compare nerve territory and dermatome →

Muscle supply is not the same as overlying skin supply. Most hamstring motor fibres are associated with the tibial component; the short head of biceps femoris is a common fibular-component exception. Posterior-thigh skin chiefly uses a separate posterior femoral cutaneous route, omitted from these selected views.

Distal branches support different movements. The tibial route serves posterior-leg and plantar targets. Common fibular branches extend toward anterior-leg dorsiflexors and lateral-leg evertors. This is a functional overview, not a sharp sensory-zone map or a way to diagnose weakness. Connect with calf force and movement →

Deeper learning · variation, sensory overlap and the foot

The level at which the sciatic components visibly separate is variable. High divisions can also have different relationships with piriformis. A single teaching view cannot represent every anatomical variant or establish a compression site in an individual person.

Cutaneous pathways extend beyond a simple anterior-versus-posterior muscle grouping. Sural, saphenous, plantar and fibular branches have different origins and overlapping territories; skin maps are not identical to motor compartments. The separate saphenous route helps explain why the sciatic system is not the nerve supply of every part of the leg.

Continue into foot support and coordinated loading →

The images are original generated teaching preparations. Their semantic anchor IDs, names, short meanings, focus geometry and accessible copy remain separate from the text-free anatomy and are reused by the enlargement view. They are not clinical scans or measured dissections.

Directed checks · 16 October 2026: Texas Tech · gluteal, thigh and posterior-knee relationships · UAMS · lower-limb nerves · Texas Tech · leg compartments and foot routes. AI-assisted source and gross anatomical checks; human medical review not performed.

Retained native regional reference · posterior lower-limb routes

Right posterior lower-limb routes; selected cream-coloured nerve routes in translucent native skeletal context. — Retained source-native supporting reference; native topology unchanged. Selected native peripheral routes; pale bones are ghosted for orientation. No independent deformation; incomplete branch coverage and fine source tube/surface detail remains illustrative / not independently verified. BodyParts3D — DBCLS (CC BY-SA 2.1 Japan); Z-Anatomy (CC BY-SA 4.0); FBX: Lluís Vinent Juanico. AllHumanBody render and changes: CC BY-SA 4.0. Full provenance in Sources below.

Teaching references: NCBI · Posterior-leg nerves · NCBI · Thigh nerves

08 / CONNECTED TEACHING

Circuits connect receptors and responses.

Principal cranial roles and reflex organisation extend the pathways without inventing missing cranial geometry.

Twelve cranial nerves serve different functions.

The directory below names principal learning roles, not every fibre component. The optic pathway is specialised central tissue; cranial nerves are not all identical peripheral cable designs. Current source geometry does not provide a verified complete cranial-nerve plate.

CN I

Olfactory

Smell-related sensory input.

CN II

Optic

Retinal ganglion-cell output in a specialised central visual pathway.

CN III

Oculomotor

Most extraocular movements, eyelid elevation and parasympathetic pupil/accommodation routes.

CN IV

Trochlear

Motor supply to superior oblique.

CN V

Trigeminal

Principal facial sensation and motor supply to mastication muscles.

CN VI

Abducens

Motor supply to lateral rectus.

CN VII

Facial

Facial expression, anterior tongue taste and parasympathetic gland routes.

CN VIII

Vestibulocochlear

Hearing and balance-related sensory pathways.

CN IX

Glossopharyngeal

Posterior tongue sensation/taste, stylopharyngeus and parotid-related parasympathetic routes.

CN X

Vagus

Visceral sensory and parasympathetic routes plus pharyngeal/laryngeal motor roles.

CN XI

Accessory

Motor supply to sternocleidomastoid and trapezius context.

CN XII

Hypoglossal

Most tongue muscle motor supply; palatoglossus is a vagal exception.

Eyes & Vision: optic pathway →Brain: brainstem and central integration →

Teaching references: NCBI · Cranial nerve roles · NCBI · Tongue innervation

A rapid response still contains integration.

A sensory ending, afferent route, central circuit, efferent route and effector form a useful reflex framework. Some circuits include a direct sensory-to-motor synapse; others use interneurons and coordinated inhibition. Reflexes are also modulated by higher circuits.

Brain: cord and reflex visual →Muscles: spindle and tendon feedback →

Teaching references: NLM · Spinal reflex circuitry

09 / CONNECTED TEACHING

Internal regulation depends on targets and receptors.

Follow autonomic origins, relays and transmitter exceptions rather than treating the divisions as universal opposite switches.

Visceral regulation is coordinated, not two universal switches.

Autonomic output regulates smooth muscle, cardiac muscle and glands. Sympathetic and parasympathetic pathways have different central origins and ganglion arrangements. Effects depend on target and receptor; not every target receives equal opposing innervation.

Compare two scoped output arrangements

A typical autonomic output uses two separate neurons. Then inspect how a terminal axon influences visceral tissue through several release sites.

Peripheral ganglion · cell-body scaleSmooth-muscle contact · closer view

Two original anatomical preparations at different magnifications: a multipolar postganglionic soma receives incoming preganglionic contacts in a peripheral ganglion, and an independent close-up shows axonal varicosities over smooth muscle. — Original generated teaching preparations at different magnifications, not microscopy or a traced continuous dissection. The CNS preganglionic soma is outside the view. Right-side particles are transmitter symbols, not a chemically identified substance. Fine synapses and cell wrapping are illustrative.

Peripheral ganglion · cell-body scale

Smooth-muscle contact · closer view

A true relay in a ganglionA preganglionic neuron has its soma in the brainstem or spinal cord. Its axon contacts a separate postganglionic neuron in a peripheral ganglion. Acetylcholine acting on neuronal nicotinic receptors supports the typical ganglionic synapse. This differs from the sensory soma beside a through-route.

Release along the targetPostganglionic terminal branches can carry multiple en-passant swellings, or varicosities. Transmitter released near smooth-muscle cells influences them through their receptors. The close-up is a representative diffuse arrangement, not a single folded skeletal-muscle endplate or a complete map of all visceral targets.

Somatic motor → skeletal muscle

One lower motor neuron connects the CNS to a skeletal-muscle fibre through its axon and specialised motor endplate. Acetylcholine evokes endplate depolarisation; muscle membrane excitation and internal calcium handling follow.

Compare the detailed, retained NMJ plate →

Autonomic → receptor-dependent response

Most sympathetic postganglionic neurons use norepinephrine at targets; many parasympathetic targets use acetylcholine. Sweat-gland sympathetic cholinergic fibres are an important exception. A target’s receptor and intrinsic activity determine its response; divisions are not universal opposite switches.

Read the transmitter and receptor exceptions →

Keep the exceptions: the adrenal medulla receives preganglionic input and releases catecholamines into blood, rather than supplying a conventional postganglionic axon to each target. Enteric networks include local circuits. Neither is forced into the illustrated two-neuron arrangement.

Origins and ganglion arrangements →Cranial and sacral pathways →A visceral target with local regulation →

Teaching focus: Somatic motor — A lower motor neuron reaches skeletal muscle through its axon.

Somatic motor

A lower motor neuron reaches skeletal muscle through its axon.

Autonomic ganglionic pathway

Preganglionic output relays to postganglionic output toward smooth/cardiac muscle or gland context.

Exceptions and local circuits

Adrenal medulla and enteric circuitry need additional explanation; do not force every route into one two-neuron rule.

Teaching references: OpenStax · Autonomic divisions · NCBI · Autonomic nervous system

Paired chains provide regional relay routes.

Sympathetic ganglia lie in paravertebral chains beside the column; other relay sites are prevertebral. Preganglionic fibres can relay at different levels or continue to other ganglia. A chain is not the spinal cord and not a single continuous neuron.

Beside the spine. Connected across levels.

Locate the paired chain, distinguish a ganglion from the connecting cord, then follow how an outflow can reach a different level or another relay. The spinal cord lies deeper, within the vertebral canal; it is not either of these gold chains.

Original anterior view toward the posterior chest wall, with paired sympathetic chains and fusiform ganglia beside vertebral bodies and posterior rib context. — Original generated regional teaching model, not a scan or specimen. The spinal cord and microscopic synapses are outside this view. This cropped thoracic segment is not a count or exact-level map of the entire chain. Fine branching and joint surfaces require separate verification.

Locate the chainThe chain lies outside the vertebral canal. A ganglion contains neuronal cell bodies; the slimmer connections carry axons between ganglia. Neither structure is the spinal cord. The opposite chain supplies another regional route, rather than forming a single cord down the midline.

Look closer at a short connection.

The neighbouring nerve has its own deeper course. A communicating branch joins it from the chain; the chain does not create the whole nerve. Compare this local connection with the larger paired arrangement above.

Detail window from the same original image: a deep thoracic nerve segment passes behind the sympathetic chain; a visible short branch connects laterally, beside a chain ganglion. — A local view of the same teaching model, not another specimen. One short connection is visible; white versus gray fibre composition cannot be identified. The complete distal intercostal route and costal groove continuity are not verified by this preparation.

Outflow levels differ from distribution levels.

Preganglionic sympathetic cell bodies lie in thoracic and upper lumbar spinal gray matter, usually described as T1–L2. White rami enter the chain at those outflow levels; gray rami connect with spinal nerves throughout the column. Axons travelling within the chain help reach regions above or below the central origin.

Evidence: UAMS · nerves of the thorax · OpenStax · autonomic connections

A route can contain a relay, or pass toward another one.

A synapse transfers influence to another neuron; a branch or crossing alone is not a synapse. Thoracic splanchnic pathways can carry preganglionic axons beyond the chain to a prevertebral relay. The adrenal medulla is a further exception, explained with the existing transmitter section. Do not treat every splanchnic nerve everywhere as the same fibre type.

Evidence: Texas Tech · thoracic autonomic pathways · OpenStax · autonomic connections

Returning to a spinal nerve reaches a different set of targets.

Postganglionic axons distributed through spinal nerves can reach cutaneous blood vessels, sweat glands and arrector pili muscles. Motor axons to skeletal muscle remain a different neuronal pathway. Visceral afferent routes can accompany autonomic nerves, but their sensory cell bodies are not the sympathetic chain’s postganglionic relay cells.

Evidence: UAMS · nerves of the thorax

Retained detailed ganglion-cell and smooth-muscle contact preparations at separate magnifications.

Change scale · where a relay occursInspect the retained cellular preparation and distinguish a synapse from a nerve branch.

Deeper learning · distribution, exceptions and what the picture cannot show

“Preganglionic” and “postganglionic” describe axons relative to a sympathetic relay. White rami include myelinated preganglionic axons; gray rami predominantly carry unmyelinated postganglionic axons. The gold surfaces in this regional image do not resolve those microscopic properties. The local short connection is therefore not individually certified as white or gray.

Axons can enter a ganglion, continue within the trunk, or pass onward toward another relay. Thoracic splanchnic and direct visceral branches are omitted from this regional preparation. Their destinations must not be inferred from a missing line or from a nearby rib. The complete intercostal nerve course and finer communicating-branch topology still need a separate anatomical view.

Regional sensory ganglia and sympathetic chain ganglia are also different structures. Compare their positions and cell-body roles before treating every swelling beside the spine as the same kind of relay.

Compare the sensory ganglion beside a root → · Keep the transmitter and adrenal exceptions → · Connect with cardiac conduction and its modulation →

Directed source and gross-structure checks: 16 October 2026. Original generated illustration with independent editable names and positions; not microscopy, a surgical map, physician review or a count of all ganglia. The same raster and semantic terms supply the full view, local window and enlarged views.

Retained native regional reference · paired sympathetic trunks

Closer native regional view of paired sympathetic nerve chains beside dark translucent vertebral context; not the whole chain. — Retained source-native supporting reference; native topology unchanged. Selected native peripheral routes; pale bones are ghosted for orientation. No independent deformation; incomplete branch coverage and fine source tube/surface detail remains illustrative / not independently verified. BodyParts3D — DBCLS (CC BY-SA 2.1 Japan); Z-Anatomy (CC BY-SA 4.0); FBX: Lluís Vinent Juanico. AllHumanBody render and changes: CC BY-SA 4.0. Full provenance in Sources below.

Bone context is ghosted to reveal source paths. This selected chain view does not show every visceral target or establish exact ganglion counts.

Teaching references: NCBI · Autonomic nervous system

Many relays lie near or within their targets.

Cranial and sacral parasympathetic pathways use ganglia near or in target tissues. The vagus supplies important thoracic and abdominal routes; sacral pathways supply other pelvic contexts. Their complete courses are not rendered in this selected peripheral atlas.

Cranial outflow

III / VII / IX / X contexts

Different pathways reach eye, glands and visceral targets.

Sacral outflow

Pelvic contexts

Distinct routes contribute to lower visceral regulation.

Target ganglia

Near / within target

Location differs from a paravertebral chain.

Teaching references: NCBI · Autonomic nervous system

Transmitters and receptors explain important exceptions.

Both divisions use acetylcholine at autonomic ganglia. Most sympathetic postganglionic fibres use noradrenaline; many sweat-gland fibres use acetylcholine. Parasympathetic postganglionic fibres use acetylcholine. The adrenal medulla releases catecholamines into blood, a neuroendocrine exception.

Ganglion

ACh / nicotinic receptors

The shared preganglionic transmitter does not imply identical target effects.

Effector

Receptor-dependent response

Muscarinic and adrenergic receptor contexts differ.

Adrenal medulla

Circulating signal

Not another ordinary long postganglionic nerve ending.

Teaching references: NCBI · Autonomic nervous system · PubMed · Neural sweat secretion review

Internal targets coordinate with other systems.

Cardiac pacemaking has intrinsic mechanisms modulated by nerves. Gut circuits organise local activity with autonomic influence. Pupillary and glandular responses use specialised routes. Visceral control operates together with hormonal and local tissue signals.

Heart

Rate / conduction context

Autonomic modulation is not the sole source of each heartbeat.

Gut

Enteric circuits

Local networks interact with sympathetic and parasympathetic inputs.

Glands / vessels

Target-specific receptors

Responses are not uniformly opposite in every tissue.

Heart →Stomach →Eyes & Vision →

Teaching references: NCBI · Autonomic nervous system · NLM · Enteric nervous system

10 / CONNECTED TEACHING

Connect the model with its evidence and limits.

Different representations answer different questions. Established related chapters extend the learning without duplicating accepted anatomy.

An anatomy mesh and microscopy answer different questions.

A render shows source-recorded regional paths. Histology reveals fascicles and connective boundaries; electron microscopy resolves axon and myelin detail; labelled fluorescence identifies molecular distribution. None of the controlled illustrations is a patient scan or measured specimen.

Regional source render

Spatial anatomy

Native source mesh, limited branch coverage.

Histology / EM

Tissue and ultrastructure

Actual licensed high-resolution peripheral specimens remain a gap.

Physiology

Electrical recording

Not inferred from colour, diameter or a still rendering.

Teaching references: PubMed · Normal peripheral nerve microscopic anatomy · PubMed · Human peripheral nerve ultrastructure review

Normal-function depth with explicit source limits.

This chapter adds peripheral organisation, tissue hierarchy, myelin, signalling, roots, plexuses, limb routes, cranial roles and visceral regulation. Clinical disorders, diagnostic maps and treatment belong to a later phase. Coverage is not a fabricated completeness percentage.

Source-supported educational relationships; native source surfaces and fine illustrative tissue detail are not independently validated histology. Human medical review: not performed. Real physical-phone acceptance: not performed. No complete cranial/enteric/visceral-target geometry or measured conduction data.

Teaching references: Z-Anatomy · Source licence and third-party exclusions · PubMed · Normal peripheral nerve microscopic anatomy

EDITORIAL RECORD

Sources & Editorial Status

Source-supported scope

Peripheral organisation, tissue hierarchy, myelin, signalling, roots, plexuses, limb routes, cranial roles and visceral regulation. Existing normal-function knowledge remains intact. Independent references support broad relationships; no source illustration or private-book prose is reproduced.

Representation limits

AI-assisted original teaching. Generated tissue and root preparations are not acquired histology, patient scans or surgical maps. Fine membranes, nuclei, channels, counts and tiny branches remain illustrative. Native regional renders are supporting references, not complete premium anatomy. Verified complete cranial geometry and autonomic routes remain gaps. Human medical review: not performed.

Regional source attribution

BodyParts3D — The Database Center for Life Science — CC BY-SA 2.1 Japan; Z-Anatomy — The open source atlas of anatomy — CC BY-SA 4.0; FBX export by Lluís Vinent Juanico. AllHumanBody selected native peripheral and skeletal objects, changed visibility, camera, lighting and materials, and exported proportional rasters. Regional derivatives: CC BY-SA 4.0. Mixed-licence third-party brain, cranial, ear and kidney meshes were excluded. Application code is not asserted to be licensed as source artwork.

Revision: nervous-system-english-2026-10-02-deep-v1. Stable local key: ahb_ch_nervous_system_english_v1. No new CMS entity, publication-state change or fabricated model mapping. Text-free masters and editable labels remain separate. Fine generated anatomy, human medical review and physical-phone acceptance are not certified. Educational only; not diagnostic or surgical guidance.